This invention relates to improvements in steering column assemblies.
Steering column assemblies for automotive vehicles and the like are increasingly required to be adjustable for rake and, in many cases, reach. This requires the column shroud, within which the steering column shaft attached to the steering wheel is rotatably located, to be fixed to the vehicle by a clamp mechanism which can be locked and unlocked to either prevent or permit adjustment of the column shroud position respectively.
One common arrangement uses a telescopic column shroud which comprises two tubes which slide one inside the other to permit reach adjustment. A fixing rail welded to one of the tubes is secured to a support bracket by the releasable clamp mechanism. Rake adjustment can be achieved by providing a support bracket which includes vertically extending slots through which the clamp mechanism passes. The clamp mechanism, which is secured to the fixing rail, can be moved vertically within these slots, taking the column with it to adjust rake.
A known arrangement for use in restricted spaces utilises a bracket in the form of an inverted U-shape having two arms depending from a base which have the vertical slots formed therein. The clamp mechanism includes a bolt which passes through the slots to link the arms together and the column is located between the arms.
The clamp mechanism typically comprises a cam mechanism that acts between a fixed part of a clamp pin and a part of one of the arms. The cam mechanism comprises a fixed cam part that is prevented from rotation by engagement of an anti-rotation feature in a slot in the arm and a rotating cam part that is typically secured to a locking lever. Both the fixed and rotating cam parts share a common axis with the bolt, the rotating cam part rotating about the axis of the bolt. The anti-rotation feature is shaped so that the fixed part cannot rotate in the slot but is free to move along the slot. For instance, it may comprise a rectangular block that protrudes from the fixed cam part away from its cam face (or cam follower), the side walls of the block fitting snugly between the side walls of the slot. Any attempt to rotate the fixed cam part will be constrained.
When locked, the shroud cannot collapse because it is clamped securely to the bracket. In some circumstances, such as a crash, it may be desirable that the shroud can collapse in a controlled manner. To achieve this it is known to fix the bracket to the vehicle using one or more frangible fasteners and to provide for an energy absorbing member which acts between the shroud or bracket and a fixed part of the vehicle when they are locked. If a crash force is applied that is sufficient to snap the couplings, the whole shroud and bracket can collapse and the collapse energy is controlled by deformation of the energy absorbing member. Other energy absorbing arrangements are known, a common trait being that they only come into play once the shroud has first been collapsed during a crash.
Whilst such designs provide increases in safety, it is also a known problem that the frangible connectors or the energy absorbing member or other arrangements could become damaged if a high force is applied to them when the clamp assembly is unlocked and being adjusted. For instance, if a driver forcefully moves the shroud to a collapsed position during adjustment, and the moveable shroud reaches the end of its travel, further movement will be resisted by the bracket. This provides a force path through to the frangible connectors the same as if the vehicle was in a crash and the frangible connectors could become damaged. The energy absorbing member may in turn also become damaged. If it springs back when the force is released the damage could go unnoticed, and the steering would perhaps not function as intended in a real crash.